1. Field of the Invention
The present invention relates to retractable pens, pencils and similar writing instruments.
2. Background of the Invention
The present invention relates to a mechanism for extruding and retracting the writing member of a writing instrument of the kind having such a writing member contained in the front part of a cylinder and energized backward by a spring between the front of the cylinder and the writing member. The writing instrument has a working element contained in the rear part of the cylinder used to press the back of the writing member to move the writing member forward. Such a writing instrument is set for writing by pressing a clip member to actuate the working element, which in turn moves the writing member forward to protrude the tip of the writing member from the opening of the cylinder. The writing instrument is restored to the non-writing condition by releasing the clip member from being pressed to retract the writing member into the cylinder.
Japanese Utility Model No. 5657/72 contains a disclosure of an extruding/retracting mechanism for use in an writing instrument wherein it has been so arranged that a writing member contained in a cylinder can be retracted by pressing a clip member fitted to the cylinder.
The aforesaid extruding/retracting mechanism is assembled so that the base of the clip member is fastened with a pin in the cylinder and is movable with the pin as a fulcrum. Further, an inclined cam surface is mated with the incline of a dowel fitted to the rear end of the writing member. In operation, the front end of the clip member is radially depressed to press the incline of the dowel, which slides forth to move the writing member forward. The top face at the front end of the base of the clip member is caused to abut against and mate with the top face at the rear end of the dowel beyond the incline of the dowel in order to make the writing member ready for writing. On the other hand, the rear end of the clip member is radially depressed downward and simultaneously its front end is lifted to release the above described mated state to move back the writing member so as to restore the writing member to the non-writing condition.
In the conventional extruding/retracting mechanism, the stroke causing the writing member to axially move forward is dependent on the length of the incline of a cam at the front end of the base and therefore there is a limit upon extending the moving stroke. Accordingly, the writing member has to move back and forth within a short stroke. While the writing member contained in the cylinder is in the non-writing condition, the front end of the writing member is held close to the opening at the end of the front end of the cylinder. Then if the writing member for use is a ball-point pen, marker or the like, the drying-up of the tip of the writing member or the contamination thereof because of foreign substances as dust sticking thereto tends to cause trouble. Moreover, since the top face at the front end of the base is attached to that at the rear end of the dowel to maintain the writing member in the writing condition, a sufficient contact area is unavailable. Because not only its resistance to the applied writing pressure but also its practical long-term utility is poor, its durability is unsatisfactory.
Further, as the writing member is extruded and retracted by moving up and down the clip member with the pinned spot as a fulcrum in the aforesaid mechanism, the stress is concentrated in the location of the pinn and the writing member does not demonstrate practical durability when used repeatedly.